This invention relates to the field of network analysis, and in particular to a method and system for assessing the survivability of a network under a variety of fault conditions.
Network simulators are commonly used to assess the effects of changes to an existing network. Proposed additional equipment to the network can be simulated on a model of the network to determine whether the addition achieves the intended goals; possible additional traffic demands can be simulated to determine the degradation of service that can be expected; modified configurations can be simulated to determine whether the modification improves or degrades the network's performance; and so on. In each of these scenarios, models of the traffic being handled, or expected to be handled, are used to simulate the operation of the network with the given traffic.
Network simulators are also commonly used to perform survivability analysis, to determine how well the network performs when faults occur. For such an analysis, the traffic models are simulated on the network model in a fault-free condition to establish a performance baseline, then the network model is modified to represent a given fault, and the same simulation is performed to determine the degradation in performance, if any, caused by the fault. In the presence of a fault, traffic on the network is automatically re-routed as required and as feasible, which will generally increase the length of the route between affected nodes, and causing the load at the nodes and links along the re-routed path to increase, which increases the level of congestion and consequential delays on other routes.
This process is repeated for each of a variety of hypothesized fault conditions, and the performance under each fault condition is recorded. By assessing the performance of the network under a variety of fault conditions, faults that produce substantial performance degradation can be identified, and measures taken to modify the system to reduce such degradations and thereby enhance the system's ability to perform satisfactorily should such a fault actually occur.
The simulation of modeled traffic on large network models generally consumes a substantial amount of time, and the repeated simulations for each hypothesized fault condition for a survivability analysis is very often infeasible. Also, because the testing of hypothesized fault conditions cannot be exhaustive, particularly in large networks, conventional fault analysis methods generally include a random selection of fault conditions to simulate, and/or require the user to specifically identify each particular fault conditions of interest.
Additionally, it is often the case that traffic models are not available and/or difficult to obtain. Network models are often used to perform ‘reachability’ analyses, to verify that the nodes in the network are able to communicate with each other, without regard to the actual traffic loads, and/or to perform security analyses, to verify that any communication restrictions are enforced by the elements of the modeled network. In these situations, without traffic models, conventional survivability analysis cannot be performed.
It would be advantageous to be able to perform survivability analysis without incurring the time demands of conventional network simulations. It would also be advantageous to be able to perform survivability analysis without requiring traffic models. It would also be advantageous to allow for targeted survivability analysis within large networks.
These advantages, and others, can be realized by providing a method and system that determines the first-order effects of fault conditions by propagating discrete test packets between select nodes and noting the path taken by the test packet under normal and faulted conditions. Tools are provided to create classes of node pairs of interest, and test packets are created only for select classes. The network is analyzed to identify fault conditions that are likely to impact system performance, and only these fault conditions are simulated. By providing a methodology for selecting classes of node pairs to test, and prioritizing the faults to simulate, a first-order survivability analysis of large networks can be performed efficiently and effectively. The efficiency of this technique is also enhanced by providing test packets that are representative of a wide range of possible source-destination combinations.
Throughout the drawings, the same reference numerals indicate similar or corresponding features or functions. The drawings are included for illustrative purposes and are not intended to limit the scope of the invention.